Oriented Strand Board (OSB) is an engineered structural-use panel typically manufactured from thin wood strands bonded together with resin under heat and pressure, and it is used extensively for roof, wall, and floor sheathing in residential and commercial construction. Orientation of wood strands with a typical aspect ratio (i.e., strand length divided by width) of at least 3 can produce a panel product with greater bending strength and stiffness in the oriented or aligned direction.
In the general manufacturing process for OSB, debarked logs are often heated in soaking ponds, then sliced into thin wood elements. The strands are typically dried, blended with resin and wax, and formed into thick, loosely consolidated mats or blankets that are pressed under heat and pressure into large panels. Oriented strand board is made from long, narrow strands, with the strands that comprise the face layers aligned parallel to one another. The strands in the core layers are usually aligned perpendicular to the strand alignment of the face layers, like the cross-laminated veneers of plywood. The strand length to width ratio and resulting orientation give OSB its unique characteristics and allows it to be engineered to suit different uses.
Typically, logs are debarked and then sent to a soaking pond or directly to the stranding process. Long log disk or ring flakers are commonly used to produce wood strands typically measuring 114 mm to 152 mm (4.5 in. to 6 in.) long, 12.7 mm (0.5 in.) wide, and 0.6 mm (0.023 in.) to 0.7 mm (0.027 in.) thick. These strand dimensions are currently accepted industry norms but longer strands (e.g., greater than 6 inches in length and greater than 0.030 inches in thickness) used to comprise the core layers may be better suited to improve panel performance attributes.
Green strands are collected in wet bins and then dried in a dryer. The dryer can be, e.g., a traditional triple-pass dryer, a single-pass dryer, a combination triple-pass/single-pass dryer, or a three-section conveyor. A relatively recent development is a dryer in which the strands are laid on a chain mat and the strands are held in place as they move through the dryer. The introduction of new drying techniques allows the use of longer strands, reduces surface inactivation of strands, and lowers dryer outfeed temperatures. Dried strands are screened and sent to dry bins.
The blending of strands with adhesive and wax is a highly controlled operation, with separate rotating blenders used for face and core strands. Typically, different resin formulations are used for face and core layers. Face resins are typically liquid or powdered phenolics, whereas core resins are typically liquid or powder phenolics or isocyanates. Several different resin applicators are used; spinning disk resin applicators are frequently used.
Mat formers take on a number of configurations, ranging from electrostatic equipment to mechanical devices containing spinning disks or other types of equipment to align strands along the panel's length and/or width. Most forming equipment uses the long and narrow characteristics of the strand to achieve strand alignment onto a moving caul plate or conveyor belt below the forming heads. Oriented layers of strands within the mat—face, core, face, for example—are dropped sequentially, each by a different forming head. Modern mat formers either use wire screens to carry the mat into the press or screenless systems in which the mat lies directly on the conveyor belt.
In hot pressing, the loose layered mat of oriented strands is typically compressed under heat and pressure to cure the resin. As many as sixteen 3.7 m (12 ft.) by 7.3 m (24-ft) panels may be formed simultaneously in a multiple-opening press. A more recent development is the continuous press for OSB. The press compacts and consolidates the oriented and layered mat of strands and heats it to 350° F. (177° C.) to 450° F. (232° C.) to cure the resin in 3 to 9 min. Other current techniques exit.
Design capacities of performance-rated products, which include OSB and plywood can be determined by using procedures outlined in Technical Note N375B (APA—The Engineered Wood Association 1995a). Additional adjustment factors based on panel grade and construction are also provided.
Oriented strand board (OSB) and methods for producing the same are generally known and are disclosed, e.g., in U.S. Pat. Nos. 6,136,408; 6,098,679; 5,718,786; 5,525,394; 5,470,631; 5,443,894; 5,425,976; 5,379,027; 4,364,984; 3,173,460; 4,893,415; 4,017,980; 3,098,781; 4,364,984; 4,068,991; 2,343,740; 3,308,013; 4,361,612; 3,164,511; 1,023,606; 4,058,906; 4,198,763; 3,685,959; 3,811,200; 4,194,296; and references cited therein. For example, oriented strand board (OSB) is commercially available from vendors such as Morgan Timber (Bibra Lake, Australia); Ainsworth Lumber (Grand Prairie, Canada); Ainsworth Lumber (100 Mile House, Canada); Grant Forest Products (Englehart, Canada); Louisiana-Pacific Canada (Saint Michel des Saints, Canada); Louisiana-Pacific Canada (Bois Franc, Canada); Louisiana-Pacific Corp. (Swan River, Canada); Louisiana-Pacific Corp. (Minitonas, Canada); Louisiana-Pacific Corp. (Dawson Creek, Canada); MacMillan Bloedel Ltd. (Hudson Bay, Canada); Norbord Industries Inc. (LaSarre, Canada); Norbord Industries Inc. (Val D'or, Canada); Sloan Forest Products (Ft. Nelson, Canada); Tolka Industries (High Prairie, Canada); Voyageur Panel (Boise Cascade) (Barwick, Canada); Weyerhaeuser (Ontario, Canada); Weyerhaeuser (Drayton Valley, Canada); Weyerhaeuser (Slave Lake, Canada); DLH A/S (Teastrup, Denmark); E & V Int' Ltd. (Central, Hong Kong); Louisiana-Pacific Corp. (Hanceville, Ala.); Cooley For. Prod. (Phoenix, Ariz.); Georgia-Pacific Corp. (Monticello, Ariz.); Allied Veneer Co. (Los Angeles, Calif.); Dotable Products Inc. (Chino, Calif.); Plylap Industries Inc. (Woodland, Calif.); Louisiana-Pacific Corp. (Montrose, Colo.); J. M. Huber Corp. (Commerce, Ga.); Norbord Industries (Cordele, Ga.); Langboard Inc. (Quitman, Ga.); Louisiana-Pacific Corp. (Athol, Id.); National Products Inc. (Syracuse, Ind.); Seemac Inc. (Carmel, Ind.); Robert Weed Plywood (Briston, Ind.); Louisiana-Pacific Corp. (Urania, La.); Martco Partnership, (Alexandria, La.); Martco Partnership (Morrow, La.); Weyerhaeuser Co. (Simsboro, La.); Georgia-Pacific (Woodland, Me.); J. M. Huber Corp. (Easton, Me.); Louisiana-Pacific Corp. (Houlton, Me.); Dyson Lumber Co. (Great Mills, Mo.); Kimball Co. (Longmeadow, Mass.); Louisiana-Pacific Corp. (Newberry, Mich.); Louisiana-Pacific Corp. (Sagola, Mich.);Nova Forest Products Co. (Milford, Mich.); Weyerhaeuser Co. (Grayling, Mich.); Louisiana-Pacific Corp. (Two Harbors, Minn.); Northwood Panelboard Co. (Solway, Minn.); Potlatch Corp. (Bemidji, Minn.); Potlatch Corp. (Cook, Minn.); Potlatch Corp., Grand Rapids (Grand Rapids, Minn.); Georgia-Pacific (Duck Hill, Miss.); Norbord Industries Inc. (Guntown, Miss.); Georgia-Pacific (Dudley, N.C.); Weyerhaeuser Co. (Elkin, N.C.); Horizon Trading Co. (Lake Oswego, Oreg.); Plymart Inc. (Boring, Oreg.); Timber Prod. Co. (Springfield, Ohio); Norbord Industries Inc. (Joanna, S.C.); J. M. Huber Corp. (Spring City, Tenn.); Norbord Industries Co. (Nacogdoches, Tex.); Norbord Industries Corp. (Jefferson, Tex.); Louisiana-Pacific Corp. (Jasper, Tex.); Louisiana-Pacific Corp. (Silsbee, Tex.); Georgia-Pacific (Skippers, Va.); Georgia-Pacific Corp. (Brookneal, Va.); J. M. Huber Corp. (Crystal Hill, Va.); Louisiana-Pacific Corp. (Dungannon, Va.); Eagon Forest Products (Bellevue, Wash.); Georgia-Pacific (Mount Hope, W. Va.); Weyerhaeuser Co. (Sutton, W. Va.); L P Hayward (Hayward, Wis.); and Midwest Lumber Associates (Middleton, Wis.). Additionally, oriented strand board (OSB) is commercially available from trade associations such as American Forest & Paper Assn. (Washington, D.C.); American Wood Preserves Inst. (Fairfax, Va.); American Wood-Preservers' Assn. (Granbury, Tex.); APA—Engineered Wood Assn. (Tacoma, Wash.); Forest Products Society (Madison, Wis.); Forintek Canada Corp. (Vancouver, BC); Structural Board Assn. (Toronto, Canada); and British Wood Preserving & Damp-Proofing Assn. (Derby, England).
One drawback associated with known oriented strand boards (OSB) is that they are susceptible to decomposition by both termites and fungus. The problem is especially pronounced in the south eastern corridor of the United States (e.g., Florida and Louisiana). Several pesticides and fungicides have been used in the pressure treatment of wood. The resulting pressure treated wood products are resistant to fungus and termites. However, many of these compounds are either extremely poisonous or are not suitable in the OSB manufacturing process.
Specifically, arsenic containing compounds, borates, and halogenated compounds (e.g., chromated copper arsenate (CCA), ammoniacal copper quat (ACQ), ammoniacal copper zinc arsenate (ACZA), creosote, and pentachlorophenol) have been used with limited success in the pressure treated wood industry. Arsenic is poisonous and its use has been criticized by several environmental groups. Additionally, the use of many known pesticides and fungicides to produce oriented strand boards results in an oriented strand board with unacceptable physical properties. For example, many pesticides or fungicides may undergo physical decomposition during the extreme conditions (e.g., temperature and pressure) typically experienced in the pressing stage (i.e., the step in which the resin is cured). As such, the resulting oriented strand board may not even be resistant to termites or fungal infections. Additionally, the pesticide or fungicide may not be chemically compatible with the resin. Moreover, the pesticide or fungicide may lose its effectiveness over an extended period of time (e.g., about 25 years) and under normal weather conditions (e.g., rain, snow, heat, exposure to UV light, etc.). For example, the pesticide or fungicide may leach out of the OSB over an extended period of time and under normal weather conditions.
As such, what is needed is a termite resistant OSB, a fungal resistant OSB, or a combination thereof; and processes for making the same. The termite resistant OSB, the fungal resistant OSB, or the combination thereof, should include a fungicide, pesticide, or combination thereof that retains its effectiveness (i.e., antifungal properties, pesticidal properties, or a combination thereof) during the manufacturing of the OSB. The termite resistant OSB, the fungal resistant OSB, or a combination thereof, should include an fungicide, a pesticide, or a combination thereof that retains its effectiveness over the extended periods of time typically encountered with the lifespan of the oriented strand board (e.g., up to about 25 years, up to about 50 years, or up to about 100 years). During the manufacture and over the lifespan of the OSB, the fungicide, pesticide, or combination thereof should remain stable in the presence of the resin. The fungicide, pesticide, or combination thereof will preferably be inexpensive, easy to manufacture, convenient to use, environmentally safe, and/or chemically stable.